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Finding the Fourth Proportional to 78.12, 107.70 and 61.80

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Solution

The fourth proportional to 78.12, 107.70 and 61.80 is: 85.20

Step by Step Solution

  1. Step 1: Write the proportion equation
    78.12 : 107.70 = 61.80 : x
  2. Step 2: Convert to fraction form
    78.12/107.70 = 61.80/x
  3. Step 3: Cross multiply
    78.12x = 107.70 × 61.80
  4. Step 4: Simplify right side
    78.12x = 6,655.86
  5. Step 5: Solve for x
    x = 6,655.86/78.12
  6. Step 6: Final answer
    x = 85.20

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.